The present invention relates to electronic locks, like the type used on hotel room doors. Generally, this type of lock includes: an encoded magnetic card, a card reader, a code verification circuit, and an electromechanical means for opening a lock. This type of lock allows opening when a code stored on a card is verified against a code stored in the lock. This particular lock is an improvement on Applicant's U.S. Pat. No. 4,793,898, issued on Apr. 23, 1987 (hereinafter, "the '898 patent").
In hotel applications, where multiple cards and users must access a given lock, there exists a need to provide security by allowing access only to currently valid cards. One way to provide security in hotel applications is to change the code stored in a lock when a new occupant accesses a room for the first time using a newly-issued card. The '898 patent discloses a programmable electronic lock which allows opening when a present key code is either equal to a stored lock code or is one unit greater than a stored lock code. A present key code is defined as a code which is computed by a lock from a card code stored on a magnetic card when a card is inserted into a card reader. A stored lock code is defined as the code against which a present key code is verified. If a present key code is equal to a stored lock code, a lock opens. If a present key code is one unit greater than a stored lock code, the lock opens and replaces the stored lock code with the present key code (one greater than the previous code).
In hotel room applications, a first occupant's card is invalidated with the change of the lock code. For example, when a second occupant for room 101 inserts his or her card into a room door lock, that card becomes the valid card for that lock, and the previous occupant's card is no longer valid.
The '898 invention discloses a second embodiment which allows opening and updating a lock code when a second card inserted into a lock results in a key code which is two units greater than a current lock code. This improved embodiment allows a third card to operate a lock when a second card is issued but never used.
Another function which the '898 patent discloses and the present invention improves on is the operation of a lock by different types of cards without interference between types. Examples of different types of cards are master cards (maids, porters, maintenance, bellhops) and guests' cards in a hotel. The '898 invention allows a master card to operate a lock without changing a lock code for a guest's card and vice versa. This is what is meant by preventing interference between types.
To prevent interference between types, the '898 invention reads a type code from a user's card, retrieves a stored lock code corresponding to that type of card, and compares the key code on the inserted card to the retrieved code. If the difference is within the required tolerance of one or two units, the lock code is updated to the present key code for that type of card only.
U.S. Pat. No. 5,198,643 issued on Mar. 30, 1993, in the name of Miron, discloses an adjustable electronic key and lock system which uses a microcomputer and a control program to control lock functions. To perform basic code verification, the microcomputer first compares a key level code to a lock level code stored in lock memory. If there is a match, the microcomputer next compares a key record number to a list of lock record numbers stored in lock memory. When it finds a match, the microcomputer compares a new key time stored on a card to a current key time code stored in memory to determine whether a key is new, current, or old. If the new key time is less than the current key time, the key is old and invalid. If the new key time is greater than the current key time, the key is valid and new and the microcomputer replaces the current key time with the new key time in memory. If the key times are equal, the key is valid and current. Upon validation, the Miron invention performs according to operational information stored with a particular key level, which may require further comparison before opening.